This invention relates to a conveyor shaft provided with rubber rollers, and a method and apparatus for the manufacture thereof.
Such conveyor shafts are frequently used in the textile and paper making industry, and also for the handling of sheets of paper in printer's machines and copiers. The rollers should be so mounted on the shafts as to be capable of transmitting a prescribed circumferential force to an article to be transported without slipping on the shaft. In copiers, the minimum torque to be transmitted per roller is 3 Nm. By rubber as used in the present specification and claims is to be understood any elastomeric material.
For the manufacture of the shafts referred to above, various methods are known.
According to a first prior method, elastomeric rollers are secured to separate sleeves by means of adhesive or otherwise. The sleeves have a tapped hole therein, and a sleeve provided with a roller is fixed to the shaft by means of a screw. The sleeves used should be accurately machined. This method of manufacture is a highly laborious one and hence expensive.
In a second method, sleeves provided with an elastomeric roller are slipped on to a shaft, whereafter the shaft is knurled at the places where the rollers should ultimately be positioned. After the knurling, the rollers are laterally shifted and clamped on the knurled areas. The knurling of the conveyor shaft requires special machinery. This method is only feasible from an economic point of view in the case of large batches. Even so there is the drawback that it is necessary for the rollers, which are produced separately, to be first temporarily fixed on the shaft in a position next to their ultimate, knurled place of attachment.
In order to avoid the use of a special knurling machine, according to a third known method, the rubber rollers are vulcanized direct on the conveyor shaft. The shafts are placed in a mould, in which they serve as a core. The cylindrical chambers around the core are filled with liquid rubber or a like elastomeric material, which is subsequently vulcanized at a suitable temperature. To promote good adherence of the rubber to the shaft, the latter is previously degreased, and at the places where the rubber is to adhere to it, roughened and covered with a layer of adhesive. After the vulcanization of the rubber, the shaft is taken from the mould, any rubber leaked along the shaft is removed, and the rollers are ground and the shaft nickel-plates and, if necessary, straightened.
It is true that, in this way, a firm connection between the rubber roller and the conveyor shaft is produced, but every shaft requires a different mould, which must have a rubber supply channel for every roller. These supply channels are therefore necessarily of some length, and this in turn requires a relatively large excess of rubber. Furthermore, the shafts can only be made of materials resistant to the vulcanization temperature prevailing in the mould, which ranges from about 160.degree. to about 190.degree. C.